Black is actually a very easy color to match with because it can serve as a neutral or it can be a bold priority color.

With leather sofas, decide if you prefer monochromatic color themes, and you want to keep it black and white, or add pops of color throughout your space.

For accessories I would bring in area rugs, throw pillows for the sofa, wall art, window treatments, and depending on how much display area - bring in color in your bookshelves, side tables and lamp shades.

Here are a few idea books for black interiors to give you some inspiration:

http://www.houzz.com/ideabooks/10095/list/Brilliant-Black

https://www.houzz.com/magazine/seeing-style-in-black-and-white-stsetivw-vs~1232